Migraine afflicts 20% of the population and is 3x more common in females. Understanding the mechanisms of migraine pain has led to the recent development of more effective acute medications. In contrast, prophylactic drugs belonging to distinct therapeutic classes (valproate, topiramate, amitriptyline, propranolol and methysergide) have been discovered empirically, and each of them only suppresses attacks by approximately 50%. Because prophylactic therapy is indicated in patients with 3+ days/month of headache-related disability, it is essential to improve migraine-preventing agents by first identifying relevant tissue or drug targets. In preliminary experiments, we discovered that chronic daily administration of each drug suppressed the susceptibility to cortical spreading depression (CSD), a poorly understood, slowly propagating electrophysiological event. Acute treatments were ineffective in this model and longer-term treatments (2-3 months) appeared more effective in preliminary experiments. Based on these observations, we propose 4 specific aims to test the hypothesis that prophylactic drugs suppress CSD as a fundamental mechanism contributing to migraine prophylaxis. To our knowledge, this is the first coherent target identified for migraine prophylaxis. The first aim proposes to establish the dose and time characteristics for drugs successfully tested so far in this model, and to expand the list of tested drugs in an attempt to establish a correspondence between animal and human drug treatments and to validate the rodent model. Aim 2 will build upon this information to determine whether overlapping patterns of gene expression within cerebral cortex explain common mechanisms important for CSD suppression after chronic treatments using optimized doses and times determined in Aim 1. In order to improve treatment for a migraine subtype (Familial Hemiplegic Migrainel), Aim 3 proposes to determine whether the effective drugs tested to date suppress CSD threshold not only in wild type animals, but also in genetically-engineered mice expressing a knock-in human mutation encoding the alpha-1 subunit of Cav2.1 (P/Q calcium channel). This mutation causes a severe migraine subtype (FHM1) and renders mutant mice more susceptible to CSD than wild type. There is emerging evidence implicating sex hormones as an important determinant of cortical excitability. Aim 4 proposes to build on preliminary data showing that estrogen withdrawal (but not estrogen administration itself) increases the susceptibility of rat cortex to CSD. We propose to explore the extent to which estrogen contributes to CSD threshold in rats, and therefore, possibly in adult human females as well. Taken together, these aims are seeking novel information impacting our understanding of migraine and its prophylaxis, and data to evaluate the validity and merits of a potentially useful animal model for screening drugs as candidates for migraine prophylaxis. [unreadable] [unreadable] [unreadable]